366 THE PALEONTOLOGY OF MINNESOTA. 
[Schizotreta minutula. 
thirteen to fifteen in the space of 2 mm. Dorsal valve depressed-convex. Ventral 
valve strongly elevated at the apex, perforate; posterior slope rapid, convex; anterior 
slope flat, or slightly concave. Pedicle opening short, narrow, oval and surrounded 
by an elevated margin. In the interior, on each side of the pedicle area, are situated 
the very narrow posterior adductor scars. The margin of this valve is distinctly, 
but slightly reflexed, producing a broad, shallow groove along the outer margin of 
the natural casts. 
This species differs from Discina circe Bi\\iiags=07-biculoidea lamellosa Hall, in 
having the ventral valve more elevated, while in the latter it is the shallower valve 
that has the pedicle opening. The apices of the valves also are much more excentric 
in S. 2)elopea than they are are in Hall's species, being very nearly central in the 
latter. From Schizotreta conica Dwight, and S. ovalis Hall, it differs in being in outline 
and not narrowly oval. 
Formation and locality. — Not uncommon in the Galena limestone, just above the Galena shales, 
in the quarries at Mantorville and at Old Concord, Minnesota. Also from the same formation at 
Dubuque, Iowa, and Neenah, Wisconsin. From the Salmon River (Hudson River) formation at Spring 
Valley, Minnesota. Also in the Trenton limestone at Montreal, Canada. 
Collectors. — A. D. Meeds and the authors. 
Mus. Reg. Nos. 263, 296, 7688-7690. 
Schizotreta mindtula, n. sp. 
a 1^ 0 A 
Fig. 28. o, dorsal valve; b, ventral valve; c, profile viev?; d, interior of dorsal valve: all x 18. 
Description: Shell minute, nearly circular in outline, marked by numerous, 
delicate concentric lines of growth and sometimes a few radii, in the anterior 
region; valves about equally convex. Ventral valve with a minute circular pedicle 
opening in the apex of the shell. Area posterior to the dorsal beak more excavated 
than that of the other valve. 
Interior of the dorsal (?) valve apparently with two pairs of muscle scars, the 
posterior pair the larger, diverging forward and situated one on each side of the beak 
cavity; the other pair is placed medially near the lateral margin. 
Dimensions, iV of a millimeter in length. 
This little species is the smallest adult brachiopod from paleozoic rocks known. 
Individuals occur in abundance associated with stems of Diplograpiiis, to which they 
were probably attached. This may account for their small size. 
Formation and locality .—FTom the lower portion of the Hudson River group near Granger, Minnesota. 
Mus. Reg. No. 8392. 
